(list 1 (list 2 (list 3 4))) ;; => (1 (2 (3 4)))


;;   [*][*]--->[*][/]
;;    |         |
;;    v         v
;;   [1]       [*][*]--->[*][/]
;;              |         |
;;              v         v
;;             [2]       [*][*]--->[*][/]
;;                        |         |
;;                        v         v
;;                       [3]       [4]


;;      (list 1 (list 2 (list 3 4)))
;;           /               \
;;          1          (list 2 (list 3 4)) 
;;                        /           \ 
;;                       2          (list 3 4)
;;                                   /      \
;;                                  3        4
